1. Field of the Invention
The present invention relates to a method and apparatus for the identification and classification, on the basis of a physical property, of randomly distributed piece goods which are in a state of translatory motion, wherein the path of travel of the piece goods is observed with a detector scanning the path transversally and indicating the wanted physical property, the said detector generating an electric signal proportional to the observed physical quantity at each spot of the scanning line, with the resolution capacity of the detector.
2. Description of the Prior Art
One of the most important needs of various fields of economic life is the classification of products which are manufactured or processed. The result and final aim of this classification is the mechanical separation of groups of pieces on the basis of the desired properties of the pieces, a procedure which can be called sorting. Classification takes place on the basis of either a measured physical quantity of mere observation.
Very commonly, classification is based on visual observation, wherein a person, on the basis of information visually obtained, decides to which class a piece good belongs, and thereafter carries out the necessary sorting. Usually piece goods travel as a continuous stream past the observer. Sorting is thus very strenuous work and cannot be performed continuously without adverse effects. One example is hand picking of crushed material in the ore-refining industry, wherein the desired objects are hand picked from crushed material on a conveyor belt. The criterion of classification may in this case be the color, size, or other visually observable physical property of the individual piece objects.
After video devices became known and reliable, TV cameras have been introduced for making optical observations. Depending on their structure, cameras are capable of detecting in the scanned area at least the same nuance differences as the human eye. The physical manifestation of the detection is an electric signal which is obtained from the camera and is proportional to the visual intensity of the scanned object. When the camera scans linearly the area to be described, the differences in intensity between the different spots on the scanning line are manifested analogously in the form of the said electric signals. Depending on the structure of the camera, i.e. in this case on its discriminating capacity, the distance between the points on the line can be expediently great or small. For example, in connection with a so-called image TV, this discriminating capacity has been adjusted to the discriminating capacity of the human eye, which is about 0.02 degrees. Camera tubes used for this purpose include Orthikon, Plumbikon, Vidikon, etc.
Other types of detectors may also be used, depending on the type of physical phenomenon which is being detected. Thus, for example, the temperatures of spots on the scanning line can be detected using an infrared detector, on their radioactive state with a Geiger counter. Separate detectors have been developed for each physical property. What they all have in common is that they generate an electric signal which is proportional to the intensity of the observed physical property and makes it possible to draw conclusions regarding the quality of the object.
The analog electric signals obtained from the detector can, suitably amplified and converted, be used directly for activating a meter or a plotter. In this case the measuring instrument may be calibrated to indicate the mean values, extreme values, or other required values of the observed physical property. The signals, suitably converted, may also be used directly for process control, in either analog or digital form. It is also known to analyse digitalized signals, in a computer in order to obtain information on the scanned object. In this case the computer is programmed to calculate the desired information on the basis of the input signals obtained from the detector and digitalized in a subsequent step. This is possible and known in the case of objects of detection which, within the detection area of the detector, appear more or less systematically, with small deviations as regards their positions and physical properties.
One example of the processing of information of the latter type is the classification of postal parcels and letters. The objects to be classified travel in this case on a conveyor belt past an optical detector or a TV camera as a continuous stream, at distances of approx. 2 cm from each other. The objects either have a certain code stamped on them in advance at a certain place and the detector indicates this code, or the detector indicates directly a postal code number typed at a certain place. In this case the detector is capable of generating electric signals with the aid of which a darker code or postal code number can be recognized against a lighter background.
In classification in which the objects appear randomly distributed on a conveyor belt or in which the objects cannot in advance be provided with appropriate codes for identification and they themselves do not include any systematic characteristics to facilitate indentification, the above system cannot be used. Such classification needs include the classification of natural products such as crushed rock and ore, root vegetables, timber, foodstuffs to be preserved, and other unrefined products. In such cases the classification apparatus must meet the following requirements:
In the absence of codes or systematic characteristics to facilitate identification, it is necessary that the identification can be performed on the basis of identification criteria which are randomly distributed. For example, in the sorting of mail, a method is so far not known which could identify an object on the basis of a hand-written postal code number.
Since the physical properties used for identifying the objects are of different types, i.e. the identification criteria can vary by their basic character, the apparatus must be capable of "learning". This means that it must be capable of determining the classification criteria of an object on the basis of information obtained from reference objects previously run through the apparatus. In the sorting of mail, the apparatus is capable of identifying object only on the basis of a certain code or machine-typed postal number. The same apparatus cannot easily be adjusted to identify an object on the basis of its size or color, for example.
Owing to the random distribution of the objects on the conveyor belt, the apparatus must be capable of identifying each object as a whole and to process the data obtained from the detector within the time period that the object resides on the scanning line of the detector, i.e. in the real time. After the object has passed the detector, the processing unit of the apparatus now reset must be immediately ready to process a new object randomly situated on the conveyor belt after it arrives into the scanning area of the detector.
In the sorting of mail, the objects are situated in a pre-organized single row. The apparatus is capable of identifying only a code or postal code number in a certain place. Furthermore, the apparatus need not shift its scan from one place to another in the transversal direction of the conveyor belt. If it is desired to process several rows of objects, there has to be a separate apparatus for each row.
As regards the classification of crushed material in the ore-refining industry by video devices, the state of the art is primarily illustrated by Canadian Pat. No. 923,601. According to this patent, randomly oriented objects are illuminated on their path of travel by a laser beam scanning across the path of travel, and the reflection of the laser beam from the object surfaces is received by a photomultiplier tube. The property of the light reflected is proportional to the property of the reflecting surface. In the detector, the light signals are converted, by known means, to analog electric signals, which thus contain information regarding the illuminated objects. In the subsequent electronic devices, the electric signals are digitalized in a known manner to form one-bit binary key numbers describing the objects.
The known method is characterized in that the path of travel scanned by the detector is divided electronically into fictive flow channels in the travel direction and that each channel has its own fixed electronic devices. Since the objective of i.e. the removal of unacceptable specimens from a heterogenous flow of objects, the number of fictive flow channels, i.e. electronic channels, correspond to the number of rejecting means. Consequently the classification is inaccurate, because the electronic system of each channel summarizes two or more objects on the same scanning line which means that all of them are rejected or accepted as a whole, though some of them may differ.
Another disadvantage consists of the fact that the system is not self-learning, i.e. it is not capable of forming, on the basis of reference objects run past the detector, the criteria necessary for the classification. The class criteria therefore have to be set into the system manually.